An electrical potential difference between two electrodes located on opposite sides of an elastomer body may generate an electric field leading to a force of attraction and thus a deflection of the elastomer body under influence of Coulomb forces between the electrodes. Such composites of electrodes on an elastomer body can be used in various ways for actuation and sensing purposes. Used as a transducer, they are sometimes referred to as electroactive polymer transducers (EAP-transducers), or artificial muscles.
Typically, it is desired to provide compliance of the transducer to deflect in a specific direction. This is typically referred to as an anisotropic structure. To provide anisotropy of the transducer, a deflection control structure is introduced. The deflection control structure can be a rigid member which is applied to the elastomer body to limit deflecting in certain directions or the deflection control structure may be constituted by the electrodes which are formed so that deflection is primarily possible in specific directions.
U.S. Pat. No. 6,376,971 discloses a compliant electrode which is positioned in contact with a polymer in such a way, that when applying a potential difference across the electrodes, the electric field arising between the electrodes contracts the electrodes against each other, thereby deflecting the polymer. Since the electrodes are of a substantially rigid material, they must be made textured in order to make them compliant.
U.S. Pat. No. 6,376,971 discloses a planar compliant electrode being structured and providing one-directional compliance, where metal traces are patterned in parallel lines over a charge distribution layer, both of which cover an active area of a polymer. The metal traces and charge distribution layer are applied to opposite surfaces of the polymer. The charge distribution layer facilitates distribution of charge between metal traces and is compliant. As a result, the structured electrode allows deflection in a compliant direction perpendicular to the parallel metal traces. In general, the charge distribution layer has a conductance greater than the electroactive polymer but less than the metal traces.
Other EAP transducers are described e.g. in US 2004/0012301 in which a waved section is provided in a body of an elastomer material. The waved shape provides compliance of the transducer in a specific direction.
The structure or shape of the deflection control structure, and thus the designed anisotropy of the known transducers are typically provided in relatively complicated processes, e.g. involving coating of various layers in a specific micro pattern. This is complicated and may cause faults in the structure and thus reduced performance of the transducer, not least when the deflection control structure is constituted by the electrodes of the composite material.